Gellable aqueous compositions containing polymers with special chelating functional groups useful for recovering oil from an oil field

Abstract

Gellable compositions containing: (a) water; (b) a water-soluble organic polymer bearing special chelating functional groups; (c) a multi-valent metal ion capable of causing the polymer to crosslink, are useful to recover oil from a oil field. Said compositions make it possible gels to be obtained which are endowed with improved physical properties and show a higher stability under the conditions prevailing in the oil field.

We claim: 
     
       1. An aqueous gellable composition comprising: (a) water;   (b) a water-soluble organic polymer crosslinkable by means of a multi-valent ion, consisting of acrylamide units and units bearing chelating functional groups, and, optionally units which are copolymerizable with acrylamide, said units bearing chelating functional groups represented by the formula ##STR21##  in which R is H or CH 3  ;   X is phenylene, --(CH 2 ) n  -- where n is within the range of 1 to 4, ##STR22## Y is selected from the group consisting of ##STR23##  in which M is H, an alkali metal or NH 4  ; Z is OH or COOM, and the substituents on the benzene ring are in the ortho position to each other, wherein said polymer has a weight average molecular weight of from 200,000 to 20,000,000 and wherein said units of formula (I) are present in an amount within the range of from 0,7 to 20 mol percent with respect to the acrylamide units;   (c) a multi-valent ion capable of causing the polymer to crosslink selected from the group consisting of Cr 3+ , Al 3+ , Ti 4+ , Zr 4+ , Sn 4+ , Zn 2+ , Y 3+   and B 3+  ; wherein the concentration of (b) in (a) is within the range of from 1000 to 50,000 ppm, the concentration of (c) in (a) is within the range of from 10 to 5000 ppm and the weight ratio of (b) to (c) is within the range of from 1:1 to 1000:1.     
     
     
       2. The composition according to claim 1, wherein the units of formula (I) are present in amounts within the range of from 0.7 to 6 mol % with respect to the acrylamide units. 
     
     
       3. The composition according to claim 1, wherein the concentration of (b) in (a) is within the range of from 1000 to 30,000 ppm, the concentration of (c) in (a) is within the range of from 25 to 500 ppm and the weight ratio of (b) to (c) is within the range of from 5:1 to 500:1. 
     
     
       4. A composition according to claim 1, wherein X is selected from the group consisting of --(CH 2 ) n  -- where n is within the range of from 1 to 4, ##STR24## 
     
     
       5. A composition according to claim 1, wherein X is phenylene. 
     
     
       6. A composition according to claim 1, wherein Y is ##STR25## 
     
     
       7. The composition according to claim 1, wherein Y is selected from the group consisting of: ##STR26## wherein M is H an alkali metal or NH 4 . 
     
     
       8. The composition according to claim 1, wherein Y is selected from the group consisting of: ##STR27## wherein M is H or alkali metal an NH 4 , and X is ##STR28## 
     
     
       9. The composition according to claim 1, wherein Y is the group: ##STR29## wherein M is H an alkali metal or NH 4 , and X is ##STR30## 
     
     
       10. The composition according to claim 1, wherein the (b) polymer consists of acrylamide units, units bearing chelating functional groups, and units which are copolymerizable with acrylamide. 
     
     
       11. The composition according to claim 10, wherein said units copolymerizable with acrylamide are selected from the group consisting of methacrylamide, sodium 2-acrylamido-2-methyl-propane-sulfonate, N-vinyl-pyrrolidone and N-vinyl-acetamide. 
     
     
       12. A composition according to claim 1, wherein the multi-valent ion is B 3+   and wherein units of formula (I) are selected from the group consisting of: ##STR31## where M is H, an alkali metal or NH 4  and R is H or CH 3 . 
     
     
       13. A composition according to claim 1, wherein the multi-valent ion is Cr 3+ . 
     
     
       14. A composition according to claim 1, wherein the multi-valent ion is B 3+   and Y is selected from the group consisting of: ##STR32## in which M is H, an alkali metal or NH 4 , and the substituents on the benzene ring are in the ortho position to each other. 
     
     
       15. A process for modifying the permeability of an oil field comprising injecting the aqueous gellable composition according to claim 1 into the oil field. 
     
     
       16. A process for fracturing an oil field comprising injecting the aqueous gellable composition according to claim 1 and a support material into the oil field. 
     
     
       17. The process according to claim 16 wherein said support material is sand.